Edge deformation effects on sensitivity and selectivity performance of graphene quantum ring gas sensor

Abstract

To explore the edge deformation effects on the performance of a graphene quantum ring gas sensor, we considered an armchair hexagonal graphene ring connected to two semi-infinite armchair graphene nanoribbons. We calculated the current through the graphene ring upon exposure to CO, NO, CO2, and NH3 gas molecules. It is shown that the behavior of current vs bias voltage depends on the inner and outer radii, and it is independent of the graphene quantum ring width. The effect of temperature resulting from nonequilibrium Green's function (Fermi–Dirac distribution) related to leads has been investigated. The substantial finding is that the current value remains unchanged up to room temperature at a perfect graphene quantum ring and, indeed, the sensor performance is unrelated to temperature. In a deformed graphene quantum ring, the influence of temperature on sensor performance is insignificant so that it is ineffective. Furthermore, the deformation in the edges can be accidental in the formation process, which we have simulated by randomly removing the atoms of the edges, or deformation can be manual, which was simulated by removing successive edge atoms from the ring sides. In the presence of edge deformation at a constant voltage, the difference between current values related to adsorption of NO, CO, and NH3 gas molecules and the pristine ring increases. In fact, the edge deformation improves the selectivity and the sensitivity of the graphene ring gas sensor. Single vacancy and double vacancies decrease the graphene ring sensor's performance. This underlines the importance of precision in the fabrication of nonedge parts of a graphene ring, although edge deformation is worthwhile in the improvement of the gas sensor.